1. Field
The present disclosure relates to systems and methods of modifying a compressed data stream to be decoded at a decoder.
2. Description of Related Art
Video information, typically comprising a sequence of picture frames, can be compressed to form a digital data stream for storage and transmission. Some of the compression standards that have attained widespread use for compressing and decompressing video information are the Moving Pictures Expert Group (MPEG) Standards for video encoding and decoding, in particular MPEG-2. MPEG Standards are used for various applications of storage, transmission and display of video information, such as optical storage systems, digital versatile disc (DVD) technology, and digital television (DTV) broadcasts. While decoding a MPEG data stream, the decoding complexity may vary from frame to frame. It may occur that the decoding complexity is higher than a capacity available at a decoder, as a decoder might generally not be equipped to deal with peak loads. In such cases, the decoder will be unable to decode the complete picture. Consequently, the output picture may abruptly suffer from quality degradation. In order to adapt the decoding complexity of a compressed data stream of video information to the available capacity at a decoder and to obtain an optimum picture quality at the output, several solutions have been suggested in the prior art.
A method and system for decoding a stream of video data with a modified decoding process at the decoder resulting in a dynamic adaptation of complexity is known from U.S. Pat. No. 6,631,163. This patent describes a method of dynamically setting a threshold value for a scalable module within a MPEG-2 video decoder system. One of the embodiments of this prior art comprises a scaling application that selectively decodes only those bi-directionally predictable blocks that meet a certain threshold and to discard those bi-directionally predictable blocks that do not meet the threshold. The threshold is dynamically adapted to changing resource levels and to fluctuating input data that occur in a system. An adjusted threshold value based on a first group of pictures (GOP) is used for decoding a second GOP.
In the prior art mentioned above, a threshold value is dynamically set for a scalable module within a decoder system. Estimating the complexity and modifying a method of decoding at the decoder is a delayed reaction. Often, region dropouts occur in essential parts of the picture, resulting in annoying artifacts to the viewer. Moreover, using a threshold value based on a previous GOP to decode a current GOP could result in distortion of unexpected regions in the output picture sequence. In other words, the prior-art method noticeably degrades a video output quality.